The invention relates to a bypass valve having the features set forth in the preamble of claim 1.
Such bypass valves, also called pressure balances, are known and control the supply flow to at least one directional control valve in such a manner that the pressure difference present at the valve and obtaining between the valve input and output is kept constant even when pressure fluctuations of the working pressure occur. Thus, the working rate remains constant even with varying working pressure.
In the attempt to increase the flow rate through a valve of specific nominal width an increased pressure difference at the valve is necessary and this simultaneously requires an increase in the regulating range of the bypass valve. A larger force is therefore necessary to open the pressure balance.
It is known (DE-PS 2,116,395) to provide the spring of a pressure balance with a biasing piston which is additionally subjected to the working pressure and thus stiffens the spring so that the pressure balance also closes at higher pressures of the pump. As long as no working pressure is present the pressure balance can easily be opened by the pump pressure against the spring force and the working medium delivered by the pump is thus connected to neutral circulation, i.e. it flows back to the tank.
The problem underlying the invention resides in constructing a bypass or shunt valve in simple manner such that in the working position of the associated directional control valve a high pressure difference is achieved for increased throughflow values and in the neutral position a low pressure difference for the pressureless circulation of the working medium.
The problem is solved according to the invention by the features set forth in the characterizing clause of claim 1.